Sustainable self-charging aqueous zinc-ion battery using calcium vanadate cathode derived from concrete waste

Self-charging aqueous zinc-ion batteries (AZIBs) are emerging as promising candidates for off-grid and autonomous energy storage, particularly where access to external power sources is limited. In this study, we report a novel AZIBs featuring a calcium vanadate (CaVO) cathode synthesized via a sustainable hydrothermal method using calcium hydroxide derived from concrete waste. Structural and morphological characterizations confirm the formation of nanostrip-shaped CaVO with high crystallinity and porosity, ideal for ion diffusion. Electrochemical tests reveal a high reversible capacity of 155 mAh g⁻¹ at 0.1 A g⁻¹, excellent rate capability, and low charge-transfer resistance. Notably, the battery demonstrates spontaneous air-driven self-charging behavior, enabled by the oxidation of reduced vanadium species through ambient oxygen via the oxygen reduction reaction (ORR). Compared to CaVO without concrete, the concrete-derived version exhibits superior redox reversibility, structural stability, and self-charging efficiency. This work introduces a cost-effective and eco-friendly approach for producing air-rechargeable AZIBs, integrating waste valorization and ambient energy harvesting for use in remote, wearable, and low-power electronics.